High-pressure hydrogen vessels and the like which are exposed to a hydrogen gas environment have a problem concerning embrittlement thereof caused by contact with hydrogen. In non-patent literature 1, one class of hydrogen damages is defined as HEE (hydrogen environment embrittlement). Reports on investigations concerning hydrogen embrittlement include non-patent literature 2, in which samples that had been regulated through a heat treatment so as to differ in strength were subjected to a tensile test in a high-pressure hydrogen atmosphere in order to elucidate tensile properties of materials placed in high-pressure hydrogen, and an influence of hydrogen pressure and strain rate is investigated. In non-patent literature 3, a material of a pressure accumulator or hydrogen compressor (chromium-molybdenum steel (SCM435)) was subjected to a fatigue test after hydrogen had been infiltrated thereinto beforehand.
It has been reported therein that even when an amount of internal hydrogen was slight, a decrease in fatigue strength and a decrease in fatigue life were observed. Furthermore, in non-patent literature 4, there is a report that a titled material which had undergone various kinds of surface finishing polishing with alumina varying from 240 grit to 0.05 μm) was subjected to a burst test in hydrogen and oxygen and, as a result, a leakage-induced failure was accelerated in hydrogen as the surface finishing became rougher, while no surface effect was observed in oxygen.
Non-patent literature 5 shows standards of The High Pressure Gas Safety Institute of Japan, and it is prescribed that a stress concentration factor due to surface roughness should be taken into account in a procedure for fatigue analysis. Non-patent literature 6 describes a method according to ASME for taking account of the stress concentration factor due to the surface roughness of a pressure vessel in a procedure for fatigue analysis Non-patent literature 7 shows values of residual stress resulting from various kinds of processing.
Incidentally, a pressure accumulator of a hydrogen gas station, for example, is supposed to undergo repeated pressure charging about 100 times per day, or about 36,500 times per year. It is therefore necessary to take account of fatigue when a high-pressure hydrogen device is designed.
In a related method for determining the fatigue of high-pressure gas facilities without taking account of a hydrogen gas environment, it is required, in the case of using a high service pressure, to multiply a stress amplitude due to fatigue by stress concentration factor due to surface roughness when a fatigue design is made (see, for example, non-patent literature 5, page 38 and non-patent literature 6, KD page 322).    Non-Patent literature 1: “Evaluation of Hydrogen Embrittlement Susceptibility of 2.25Cr-1Mo Steel for Pressure Vessel after Long-Term Service”, The Japan Pressure Vessel Research Council, 2001, pp. 2.    Non-Patent literature 2: IMADE Masaaki, FUKUYAMA Seiji, ZHANG L, WEN M, YOKOGAWA Kiyoshi (National Institute of Advanced Industrial Science and Technology, Research Institute of Instrumentation Frontier), “Hydrogen Embrittlement of SCM440 Steel in Room-Temperature High-Pressure Hydrogen Atmosphere”, Nihon Kinzoku Gakkai Shi, published on Feb. 20, 2005, Vol. 69, No. 2, pp. 190-193, Tracing 7, Table 1, Ref. 18.    Non-Patent literature 3: MURAKAMI Yukitaka (Kyushu University), “Difficult Problem in Hydrogen Utilization Technologies/How Hydrogen Lessens Strength of Materials”, Kihō Enerugī Sōgō Kōgaku, published on Jul. 20, 2005, Vol. 28, No. 2, pp. 22-29.    Non-Patent literature 4: LEWIS B A, LOUTHAN JR M R, WAGNER J, SISSON JR R D, McNITT R P, LOUTHAN III M R (Virginia Polytechnic Inst.), “The effect of surface finish on the deformation characteristics of 1015 steel at 25“C”, Met Hydrogen Syst, published in 1982, pp. 347-353.    Non-Patent literature 5: “Standards of The High Pressure Gas Safety Institute of Japan”, Chōkōtsu Gasu Setsubi Ni Kansuru Kijun KHK S 0220, published in 2004, pp. 38.    Non-Patent literature 6: ASME Boiler And Pressure Vessel Code, Section VIII, Division 3, Part KD300, p. 39.    Non-Patent literature 7: “Data for Fatigue Strength Design (II)”, Hyōmen Jōtai, Hyōmen Shori (revised 2nd ed.), The Japan Society of Mechanical Engineers, published in 1982, pp. 3-4.